Hermetically sealed containers with unitary closures are known. Such containers typically have a body portion, a neck portion, and a top or closure structure to close and seal the opening in the neck portion.
It is also known to provide such containers with means for permitting the containers to be opened by breaking off the sealed closure at the top of the container or on the neck portion of the container between the container sealed top and the container body portion.
To facilitate such opening of the container, a frangible web is typically provided in the container neck portion. The frangible web comprises a reduced thickness region in the wall of the material forming the neck portion of the container. Such a container is typically opened by twisting or bending the part of the container above the frangible web relative to the part of the container below the frangible web so as to rupture or sever the reduced thickness region of material at the frangible web.
Containers incorporating the above-described frangible web structure are typically formed from a thermoplastic material. Such containers are conventionally fabricated by blow molding and/or vacuum forming and may or may not include an insert article or stopper as part of, or in addition to, the container sealed top or closure structure.
Tvpically, the thermoplastic material is extruded as a length of parison in the form of a vertically oriented, elongated, hollow tube between the pair of main mold halves for initially forming the container body with an open top. Means are provided for maintaining the opening at the top of the length of parison in the portion of the parison extending upwardlv above the main mold means.
An extendable and retractable blowing assembly with a sealing mandrel and blowing nozzle is extended into the length of parison in the main mold halves to temporarily seal the opening. A gas is injected into the parison to mold the container with or without vacuum assist in the mold cavity defined by the main mold halves.
The main mold halves (or other mold members), along with the cooperating sealing mandrel on the blowing assembly, typically define a structure for molding the frangible web structure.
One such apparatus for molding and forming a container with a frangible web is disclosed and illustrated in U.S. Pat. No. 4,239,726. With reference to FIG. 6 in that patent, a mandrel 42, which can be equipped with a container blowing and filling nozzle, is described as being provided with an annular, ring-shaped molding surface 42 that serves to form a frangible annular web around the container hollow stem or collet 12.
Another apparatus for forming a frangible web in a container is illustrated in U.S. patent application Ser. No. 296,368, filed Aug. 26, 1981 and assigned to the assignee of the present invention. In application Ser. No. 296,368, there is disclosed an apparatus for molding a container with a closure article, such as a stopper, inserted in the container opening. The article is disposed within the container opening by means of a pick up arm that is positioned between the main mold halves. Sealing mold halves, located above the main mold halves, are subsequently closed to pinch the parison against the pick up arm above the stopper held at the bottom of the pick up arm. The sealing mold halves have an inwardly projecting frangible web forming means or flange for forming the reduced thickness region of the parison to define the frangible web.
U.S. patent application Ser. Nos. 11,149, filed Feb. 12, 1979, and 194,839, filed Oct. 7, 1980, both assigned to the assignee of the present invention and both now abandoned, illustrate a molding apparatus for producing a container. The container has a rigid dispensing tip with an orifice of a predetermined size and has a rigid but hollow cap closing off the orifice. The cap is unitary with, and connected to, the dispensing tip of the nozzle by means of a unitary, annular frangible web.
The nozzle of the container described in the above-identified U.S. patent application Ser. Nos. 11,149 and 194,839 is formed in the parison at the bottom of the main mold halves. The main mold halves have an interior cavity configuration defining an inwardly projecting flange for cooperating with a ram to form the nozzle and to form the cap structure joined to the nozzle by means of the annular frangible web.
Finally, U.S. Pat. No. 3,597,793 illustrates an apparatus for molding a container and for forming a frangible web in the container. Of interest are the embodiments of the apparatus illustrated in FIGS. 19, 22 and 24. Various forms of a mandrel are shown for cooperating with a pair of main mold halves.
In FIG. 24 of the patent, the mandrel 130 is illustrated as cooperating with the pair of molding jaws 131 to form a weakened, angularly disposed flange 132 between the neck portion 133 of a bottle and the integrally formed closure top 134.
In FIG. 23 of the patent, a mandrel 127 is illustrated with a frustoconical flange 128 which tapers downwardly and outwardly to form a pointed tip 129. The tip 129 cooperates with the tapered surface 126 of the molding jaw halves 125 to form a groove at the juncture between the neck portion of a bottle and the closure top to provide a frangible web.
Finally, FIG. 19 of the patent illustrates a mandrel 119 having a frustoconical wall 118 which extends downwardly inwardly away from a flange or pointed tip 114 to provide a groove or frangible web in the parison.
Although the above-described methods and apparatus for forming frangible webs in containers function satisfactorily for fabricating frangible webs in specific types of containers for which such methods and apparatus were intended, there is no sealing surface within the main mold that is adequate to withstand gas pressures within the main mold cavity while a container is blow molded therein. It would be desirable to provide an improved method and apparatus for forming frangible webs in the neck portion of a container by pressure-assisted molding.
Specifically, it would be desirable to provide improved control of the thickness of the formed frangible web, to provide improved sealing between the sealing mandrel and the parison, and to provide a mandrel that forms, on a consistent and repeatable basis, the frangible web with a smooth surfaced inner wall of a specified diameter.
Further, it would be desirable to provide a method and apparatus wherein the molding assembly and its maintenance could be simplified to permit the formation of the frangible web at the top portion of the main mold halves.